Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2006SUBURBAN C2500, 6.0 UREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 992 (LIGHTING SYSTEMS)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B257ACIRCUIT/SYSTEM TESTING
2006 Chevrolet Suburban C2500, 6.0 U
Circuit/System Testing
2006 Chevrolet Suburban C2500, 6.0 USECTION Circuit/System Testing
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
DTC B257A
| Circuit | AUTO | PARK | HEAD |
|---|---|---|---|
| Headlamp Switch Headlamps Off Signal BCM Terminal 17 | Ground | Open | Open |
| Headlamp Switch Park Lamps Signal BCM Terminal 8 | Open | Ground | Ground |
| Headlamp Switch Headlamps On Signal BCM Terminal 12 | Open | Open | Ground |
- Ignition OFF, disconnect the BCM connector C2 and start with the headlamp switch in the AUTO position. Use the chart above to determine when and where a ground signal should be present. Test each connector circuit listed in the chart for the proper signal.
- If voltage is present on any circuit, test that circuit for a short to voltage.
- If the circuit/connections test normal, replace the headlamp and panel dimmer switch.
- If no ground signals are present, test the headlamp switch ground circuit for an open.
- If the circuit/connections test normal, replace the headlamp and panel dimmer switch.
- If all signal functions of the headlamp and panel dimmer switch circuits test normal, replace the BCM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.